Polymer-solvent interaction parameters in polymer solutions at high polymer concentrations

Ion chromatography (IC) is widely used for the compliance monitoring of common inorganic anions in drinking water. However, there has recently been considerable interest in the development of IC methods to meet regulatory requirements for analytes other than common inorganic anions, including disinfection byproduct anions, perchlorate, and haloacetic acids. Many of these new methods require the use of large injection volumes, high capacity columns and analyte specific detection schemes, such as inductively coupled plasma mass spectrometry or postcolumn reaction with UV-Vis detection, in order to meet current regulatory objectives. Electrospray ionization mass spectrometry (ESI-MS) is a detection technique that is particularly suitable for the analysis of permanently ionized or polar, ionizable compounds. The combination of IC with MS detection is emerging as an important tool for the analysis of ionic compounds in drinking water, as it provides increased specificity and sensitivity compared to conductivity detection. This paper reports on the application of IC-ESI-MS for the confirmation and quantitation of environmentally significant contaminants, i.e. compounds with adverse health effects which are either regulated or being considered for regulation, such as bromate, perchlorate, haloacetic acids, and selenium species, in various water samples.     

Thermodynamic interaction parameters in polymer solutions and gels

Polymer-solvent interaction parameters are reported for poly(vinyl acetate)-acetone, poly(vinyl acetate)-toluene, and poly(dimethyl siloxane)-toluene systems using different techniques. Results obtained by osmotic deswelling are compared with those from quasi-elastic light scattering and small-angle neutron scattering (SANS). In gels, the latter techniques involve separation of the time-dependent from the static component of the scattered radiation+ Separation is achieved in quasi-elastic light scattering through the heterodyning properties of the light, and in SANS by subtracting an appropriate static structure factor. The interaction parameters obtained by different separation procedures are consistent with measurements using the osmotic method. © 1995 John Wiley & Sons, Inc.     

Jetting of dilute polymer solutions

Light emitting devices containing conjugated polymers are conveniently fabricated using ink-jet printing. A common problem in the processing of these materials is that the Newtonian viscosity of the polymer solution is not sufficient to describe the jetting performance because the molecular weights and concentrations employed are such that the resulting solutions are elastic. These differences in fluid elasticity levels cannot be measured using traditional techniques like dynamic mechanical experiments or the first normal stress difference in shear, but strongly impact the jetting behavior of the liquid. In this study, a variety of polystyrene solutions in DECALIN having a shear viscosity of ~5 mPa s but different elasticity levels were examined for their jetting behavior. The jetting behavior of these solutions was studied visually using drop-on-demand jetting equipment and their rheology was characterized using a custom extensional rheometer designed for measuring the elasticity of such low viscosity liquids. If elasticity effects are absent as in Newtonian liquids (corresponding to a Trouton ratio of 3) satellite drops are formed resulting in loss of liquid and poor positioning. On the other hand, if elasticity effects are very large (Trouton ratios ≫4) separation problems occur at the nozzle with undesirable “tailing.” The optimum range for stable, efficient jetting occurs at Trouton ratios in a narrow band between 3 and ~5. A very slight degree of elasticity corresponding to a Trouton Ratio around four thus seems to be optimum for the jetting process. This appears to be the first time that such a design criterion has been outlined for this process. Such an approach complements thermal techniques for elucidating the role of molecular and flow properties on the processing behavior of polymeric systems.     

Shear thinning in dilute polymer solutions

We use bead-spring models for a polymer coupled to a solvent described by multiparticle collision dynamics to investigate shear thinning effects in dilute polymer solutions. First, we consider the polymer motion and configuration in a shear flow. For flexible polymer models we find a sharp increase in the polymer radius of gyration and the fluctuations in the radius of gyration at a Weissenberg number approximately 1. We then consider the polymer viscosity and the effect of solvent quality, excluded volume, hydrodynamic coupling between the beads, and finite extensibility of the polymer bonds. We conclude that the excluded volume effect is the major cause of shear thinning in polymer solutions. Comparing the behavior of semiflexible chains, we find that the fluctuations in the radius of gyration are suppressed when compared to the flexible case. The shear thinning is greater and, as the rigidity is increased, the viscosity measurements tend to those for a multibead rod.     

Thermodynamic properties of dilute solutions of carbon monoxide in a hydrocarbon

Partial molar volumes, enthalpies, entropies, and energies have been obtained for dilute solutions of carbon monoxide in liquid benzene and in liquid n-octane up to 523 K and 15 MPa. As for (hydrogen + a hydrocarbon), the ratio $\text{a}{}_{12}\text{a}{}_{11}$ of the cohesive energy densities is independent of hydrocarbon type.     

Ultracentrifugal equilibrium measurement of high polymer solutions at elevated temperatures

To investigate the solution properties of polyethylene, which has the simplest structure of the vinyl polymers, experiments were made with a magnetically suspended equilibrium ultracentrifuge. Preliminary studies were carried out with a polystyrene–chloroform system at 25°C. and a polystyrene–methylcyclohexane system at 68°C. (which is close to the theta temperature) in order to check the difficulties involved in the flotation equilibrium in the former case and the high temperature measurement in the latter. However, no trouble was encountered in either system, and the results were discussed and compared with earlier results for polystyrene solutions. It was found that chloroform is a good solvent for polystyrene, and the measured weight-average molecular weight is somewhat smaller than the value obtained in a theta solvent. After overcoming some technical difficulties involved in studies at higher temperatures, we carried out experiments on polyethylene in α-chloronaphthalene at 130°C. The results are considered reasonable by comparison with results obtained by other methods. The sample employed, Marlex 50 of melt index 0.7, has a wide molecular weight distribution: i.e., M_z/M_w = 5.2 and M_z+1/M_z = 2.4.     

Viscosities of dilute polymer solutions in nematic liquids

A nematic fluid is characterized by five friction coefficients. When dilute polymer coils are added to the fluid, all these coefficients are modified. Three Miesowicz viscosities (measured under an aligning magnetic field) and two coupling coefficients between orientation and flow are discussed. In our calculation, elastic dumbbells are used to model the flexible polymer chains. The results are written in terms of two size parameters R_∥ and R_⊥ and two chain friction coefficients λ_∥ and λ_⊥ (the label ∥ refers to a direction parallel to the nematic axis). This could be compared to other experiments (such as translational diffusion) which measure λ_∥ and _⊥ directly. They may give useful estimates of coil conformation in nematic solvents.     

Thermodynamic properties of dilute solutions of selenium in liquid lead

The activity coefficients and activities of selenium in liquid alloys of the Pb-Se system at low selenium content were estimated from the available experimental data.     

Thermodynamic properties of dilute solutions of bismuth in liquid lead

Value of the limiting activity coefficients in liquid alloys of bismuth with lead at 673, 773 and 873 K were assessed with application of various analytical expressions.     

Thermodynamic properties of dilute solutions of antimony in liquid lead

Various methods of assessing the limiting activity coeffi cient of antimony and the area of the Henry’s Law holding in liquid alloys of antimony-lead system were considered.     

Thermodynamic parameters for the protonation of urea at different temperatures and ionic strengths

Potentiometric measurements of aqueous urea solutions (less than2.5 mol-dm⁻³ of urea) were performed at different temperature and ionic strengths (10≤T≤45°C; 0.02≤I≤0.6 mol-dm⁻³) to determine thermodynamic protonation parameters. The formation of the species U₂H⁺ was hypothesized to explain the concentration dependence of the protonation constant.     

Thermodynamics and viscosities of dilute polymer solutions in binary solvents

Experiments aimed at comparison of calculated and experimental intrinsic viscosities of PS and PMMA in some binary solvents used as eluents in chromatography are performed. The intrinsic viscosities are determined in mixed solvents of different thermodynamic qualities, including a θ solvent, in a wide composition range. The analysis of the thermodynamic and rheological theoretical equations for ternary systems allowed the interpretation of anomalies observed on the experimental curves of intrinsic viscosity versus solvent composition.     

Capillary electrophoresis of RNA in dilute and semidilute polymer solutions

We report separations of RNA molecules (281-6583 nucleotides) by capillary electrophoresis in dilute and semidilute solutions of aqueous hydroxyethylcellulose (HEC) ether in varying buffers. RNA mobility and peak band widths are examined under both nondenaturing and also denaturing conditions. From studies of sieving polymer concentration and chain length, it is found that good separations can be obtained in semidilute solutions as well as in dilute solutions. The dependence of RNA mobility on its chain length is consistent with separation by a similar to transient entanglement mechanism in dilute solutions. In semidilute entangled solutions the separation proceeds by segmental motion.